Combustion apparatus

ABSTRACT

An object of the present invention is to provide a combustion apparatus capable of certainly detecting a shortage of an amount of air relative to that of fuel gas. 
     A combustion apparatus  1  is adapted to perform a primary combustion of air-fuel mixture in an oxygen-deficient condition composed of mixture of primary air and fuel gas and further perform a secondary combustion upon supply of secondary air  67,  including a first ion current measuring element  65  positioned at a site where a flame of the primary combustion is to take place and a second ion current measuring element 66 adjacent to a secondary air supply opening  20, 21, 63,  or  64  for supplying the secondary air  67,  so as to control at least one selected from a group consisting of (a) a ratio of an amount of the primary air to that of the secondary air, (b) a total amount of the primary and the secondary air, and (c) an amount of the fuel gas based on measured values by the first and the second ion current measuring elements  65  and  66.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a combustion apparatus, and more particularly to a combustion apparatus recommended to be used in a water heater or a bath heater.

2. Description of the Related Art

A combustion apparatus is a main component in a water heater or a bath heater and in widespread use at home as well as at factories.

Recently, environmental destruction resulting from acid rain has become a grave social issue, and thus, there is a pressing need to reduce a total amount of emission of NOx (nitrogen oxides).

There is a combustion apparatus employing a combustion system called the “thick and thin fuel combustion” method adapted to be used in a small device such as a water heater and to reduce NOx emissions.

The “thick and thin fuel combustion” method is designed to produce a main flame from a lean mixed gas composed of fuel gas premixed with air of about 1.6 times the amount of the theoretical amount of air and arrange around the main flame an auxiliary flame produced from a rich mixed gas with a small amount of mixed air and a high gas concentration.

A combustion apparatus based on the thick and thin combustion is known for such a configuration as disclosed in the patent documents 1 and 2, for example.

A combustion method with a less amount of NOx emissions also includes a combustion system called the “two-staged combustion” method. The “two-staged combustion” method is adapted to inject fuel gas in an oxygen-deficient condition to produce a primary flame by igniting the gas, so as to produce a secondary flame by supplying a secondary air to unburned gas.

The patent document 3 discloses a combustion apparatus employing such a two-staged combustion method.

Patent Document 1: JP 5-118516A

Patent Document 2: JP 6-126788A

Patent Document 3: JP 52-143524A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

A combustion apparatus employing the thick and thin fuel combustion method generates a less amount of NOx emissions, being well-reputed in the market, but is disadvantageous in low Turn Down Ratio (T. D. R). Especially, a combustion apparatus employing the thick and thin fuel combustion method is disadvantageous in difficulty to burn in an area with a low heating value.

Specifically, in the thick and thin fuel combustion method, a main flame is produced from a lean mixed gas composed of fuel gas premixed with air of about 1.6 times the amount of the theoretical amount of air, as described above. The mixed gas has a low burning rate because of its leanness.

The combustion apparatus employing the thick and thin fuel combustion method is provided with a fan for generating a lean mixed gas, but the fan would become deteriorated due to years of its use, resulting in gradually reducing its blowing volume. Further, a filter of the fan would be clogged, resulting in reducing its air blowing volume. The reduced air blowing volume reduces an amount of air in the mixed gas producing a main flame, rendering the amount of mixed air approaching the theoretical amount of air. As a result, a combustion speed of the main flame becomes more rapid. Therefore, a proximal end of a flame gradually approaches burner ports across the ages. Thus, combustion in an area with a low heating value would render a proximal end of a flame approaching to burner ports, resulting in damaging the burner ports. Consequently, a combustion apparatus employing the thick and thin fuel combustion method is forced to restrict combustion in an area with a low heating value on an anticipated aging.

In addition, the thick and thin fuel combustion method imposes such a restriction as a narrow range of usable gas. Specifically, fuel gas supplied by a gas maker may be constituted by a single component, but in many cases, by a plurality of components. That causes different combustion speed depending on makers of fuel gas even if their amounts of heat generation (amounts of heat per unit volume) are the same among them.

Since the thick and thin fuel combustion method produces a main flame in an air excess condition, fuel gas having a slow combustion speed might cause blow off, resulting in unstable combustion.

In contrast, the two-staged combustion method can set a higher Turn Down Ratio than the thick and thin fuel combustion method. Further, a wide variety of fuel gas is available. However, the two-staged method burns fuel gas in an oxygen-deficient condition, resulting in unstable combustion. Provably for this reason, we found none of practical devices such as water heaters that are offered commercially and employ the two-staged combustion method.

A combustion apparatus employing the two-staged combustion method is constituted in such a manner that a burner port assembly for producing a primary flame is surrounded by an air combustion assembly for producing a secondary flame at downstream of the primary flame.

The conventional two-staged combustion type combustion apparatus for use in application other than in a water heater uses a thermocouple as a means to assess combustion condition, but the thermocouple cannot detect a shortage of air supply, and thus, an ion current measuring element (probe) for measuring ion current (also called “ionization current”) in flame is mainly employed instead of the thermocouple in recent years. Ions exist in flame, which is electrically a conductor. An ion content in a primary flame and an ion content in a secondary flame are measured, so as to calculate a difference between the two contents. That is why ion current measuring elements are necessary to be positioned at two sites of the combustion apparatus.

A water heater in recent years has been miniaturized. A combustion apparatus incorporated in a water heater has been required to be miniaturized along with that. Two ion current measuring elements positioned in a combustion apparatus would get closer to each other. Thus, ion current is more likely to flow between both of the measuring elements, resulting in having significant bad effects on assessment of combustion condition.

An object of the present invention made in view of the problems and drawbacks in the art described above is therefore to provide a combustion apparatus capable of certainly detecting a shortage of an amount of air relative to that of fuel gas.

Means to Solve the Problem

In order to solve the problems and drawbacks described above, an aspect of the present invention provided herein is a combustion apparatus adapted to perform a primary combustion of air-fuel mixture in an oxygen-deficient condition composed of mixture of primary air and fuel gas and further perform a secondary combustion upon supply of secondary air, including a first ion current measuring element positioned at a site where a flame of the primary combustion is to take place, and a second ion current measuring element adjacent to a secondary air supply opening for supplying the secondary air, so as to control at least one of supplied air and fuel gas based on measured values by the first and the second ion current measuring elements.

The first ion current measuring element penetrates through high-temperature flame front of the primary flame with the distal end situated within the primary flame. The primary flame includes unburned air-fuel mixture therewithin, being at low temperature. Consequently, the first measuring element does not reach an extremely high temperature in totality. Further, the second ion current measuring element is cooled by the secondary air. That avoids deformation of the first and the second measuring elements resulted from high temperature. Further, combustion condition of the combustion apparatus is detected and anomalous combustion is appropriately normalized.

By provision of both of the ion current measuring elements as described above, output values obtained from the first and the second measuring elements do not change in synchronism with reduction of an amount of supplied air, so as to certainly detect that an amount of supplied air is reduced.

As to the supplied air, adjustment of its supply or a ratio of distribution of the primary air and the secondary air can be controlled.

The combustion apparatus may be adapted to control at least one selected from a group consisting of (a) a ratio of an amount of the primary air to that of the secondary air, (b) a total amount of the primary and the secondary air, and (c) an amount of the fuel gas.

Such an arrangement produces an effect similar to the above-mentioned one. Further, the present arrangement controls at least one selected from a group consisting of a ratio of an amount of the primary air to that of the secondary air, a total amount of the primary and the secondary air, and an amount of the fuel gas based on measured values by the first and the second ion current measuring elements, so as to appropriately normalize combustion condition even if the combustion condition may become anomalous.

By provision of both of the ion current measuring elements as described above, output values obtained from the first and the second measuring elements do not change in synchronism with reduction of an amount of supplied air, so as to certainly detect that an amount of supplied air is reduced.

The combustion apparatus may include at least one premixer adapted to introduce thereinto the fuel gas along with the primary air to generate the air-fuel mixture in an oxygen-deficient condition, at least one air passage member of a wall shape having the secondary air supply opening for supplying the secondary air at its distal end, at least one burner port assembly arranged between two of the air passage members or between the air passage member and another wall, and at least one combustion part formed by a space enclosed by the burner port assembly and the air passage member, wherein the air-fuel mixture is discharged from the burner port assembly into the combustion part to perform the primary combustion and further perform the secondary combustion upon supply of the secondary air from the secondary air supply opening of the air passage member.

The combustion apparatus in the present aspect includes the first ion current measuring element positioned at a site where a flame of the primary combustion is to take place and the second ion current measuring element adjacent to the air supply opening, so that the both measuring elements do not reach a high temperature. Especially, the second measuring element is cooled by the secondary air supplied from the air supply opening, whereby high-temperature deformation is avoided.

Further, during a normal combustion, the secondary air protects the second measuring element from flame, thereby preventing flow of weak ion current between the first and the second measuring elements, and whereby anomalous combustion in a shortage of air is certainly detected.

Still further, in the case of detection of anomalous combustion based on measured values by the both measuring elements, the combustion apparatus is designed to control at least one selected from a group consisting of a ratio of an amount of the primary air to that of the secondary air, a total amount of the primary and the secondary air, and an amount of the fuel gas, thereby normalizing the anomalous combustion.

Another aspect of the present invention is a combustion apparatus adapted to perform a primary combustion of air-fuel mixture in an oxygen-deficient condition composed of mixture of primary air and fuel gas and further perform a secondary combustion upon supply of secondary air, including a first ion current measuring element positioned at a site where a flame of the primary combustion is to take place, an air supply port for supplying air different from the primary air to a base of the flame of the primary combustion, and a second ion current measuring element adjacent to the air supply port, so as to control at least one of supplied air and fuel gas based on measured values by the first and the second ion current measuring elements.

The combustion apparatus may include at least one premixer adapted to introduce thereinto the fuel gas along with the primary air to generate the air-fuel mixture in an oxygen-deficient condition, at least one air passage member of a wall shape having a secondary air supply opening, at least one burner port assembly arranged between two of the air passage members or between the air passage member and another wall, and at least one combustion part formed by a space enclosed by the burner port assembly and the air passage member, wherein the air-fuel mixture is discharged from the burner port assembly into the combustion part to perform the primary combustion, and wherein the secondary air supply opening is located at a base of the flame of the primary combustion.

As described above, the distal end of the first measuring element penetrates through the flame front of the primary flame to be positioned within the primary flame at a relatively low temperature, so that the first measuring element does not reach at an extremely high temperature in totality. Further, the second ion measuring element is adapted to be cooled by air. Consequently, high-temperature deformation of the both measuring elements is avoided.

The distal end of the first ion current measuring element may be curved or bent.

It is preferable that the distal end of the first measuring element is curved or bent toward upstream of flow of fuel gas.

The distal end of the second ion current measuring element may be curved or bent.

It is preferable that the distal end of the second measuring element is curved or bent toward the center of a combustion area.

The combustion apparatus may be adapted to blow air to the second ion current measuring element. By blowing of air to the second measuring element, the second measuring element is cooled by the air. That avoids high-temperature deformation. Further, air existing around the second measuring element prevents flow of ion current between the first and the second measuring elements.

The combustion apparatus may further include a memory storing a standard value relating to difference between output values measured by the first and the second ion current measuring elements corresponding to a regulation value of emission concentration of carbon monoxide.

The standard value may have a predetermined width. The center value of the predetermined width can be set at discretion, and can correspond with the above-mentioned difference between the output values. Having the predetermined width, the combustion apparatus readily determines whether combustion condition is normal or not.

The combustion apparatus may be adapted to compare a calculated value of the difference with the standard value stored in the memory.

As a result of the comparison, the combustion apparatus increases air supply and/or reduces fuel gas supply in the case that the calculated value is bigger than the standard value stored in the memory, thereby normalizing combustion of the apparatus. Further, setting a ratio of an amount of the secondary air to that of an amount of the primary air larger normalizes combustion of the apparatus.

Conversely, in the case that the standard value stored in the memory is smaller than the calculated value, a normal combustion is performed.

The combustion apparatus may define three routes through which air flows: a first route within the air passage member, a second route from between the premixer and the burner port assembly to the combustion part, and a third route through which air flows with the fuel gas, the first and the second routes being adapted to supply the secondary air, the third route being adapted to introduce the primary air, further including a memory for storing a standard value relating to difference between output values measured by the first and the second ion current measuring elements corresponding to a regulation value of emission concentration of carbon monoxide, being adapted to compare a calculated value of the difference with the standard value stored in the memory, and being adapted to increase supply of the secondary air flowing through the first and the second routes in the case that the calculated value is bigger than the standard value stored in the memory.

By such an arrangement, if the calculated value indicates anomalous combustion of the combustion apparatus, the combustion apparatus increases supply of the secondary air passing through the first and the second routes to sufficiently supply oxygen, thereby normalizing combustion.

Advantageous Effect of the Invention

The combustion apparatus of the present invention arranges the first ion current measuring element in the primary flame and the second ion current measuring element adjacent to the secondary air supply opening so as to blow the secondary air to the second measuring element.

Herein, the first measuring element penetrates through high-temperature flame front with its distal end positioned within the primary flame. The primary flame includes therein unburned gas mixture, so that the temperature is low. Thus, the first measuring element does not reach an extremely high temperature in totality. Further, the second ion current measuring element is cooled by the secondary air. Consequently, both of the first and the second ion current measuring elements are not deformed by high temperature, so as to certainly detect an anomaly of combustion caused by a shortage of an amount of air relative to that of fuel gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional perspective view conceptually illustrating a configuration of a combustion apparatus 1 of the present invention;

FIG. 2 is a perspective view of a combustion apparatus in a practical embodiment of the present invention;

FIG. 3 is a plan view of a plurality of the combustion apparatus in FIG. 2 accommodated in a casing;

FIG. 4 is a sectional view taken substantially along the lines IV-IV of FIG. 3;

FIG. 5 is a sectional view of the combustion apparatus in FIG. 2;

FIG. 6 is an exploded perspective view of the combustion apparatus in FIG. 2;

FIG. 7 is a sectional view of an air passage member of the present embodiment;

FIG. 8 is a sectional perspective view of a combustion apparatus arranged with other ion current measuring elements available in embodying the present invention;

FIG. 9 is a graph showing a relation of output values of a first and a second ion current measuring elements and an amount of carbon monoxide CO;

FIG. 10 is a view of a controlling system for controlling an amount of air and an amount of fuel gas;

FIG. 11 is a flow chart for assessing combustion condition of a combustion apparatus;

FIG. 12 is a sectional perspective view of a modified combustion apparatus in which the second ion current measuring element is located at a different position from those in FIGS. 1 and 8;

FIG. 13 is a flow chart for assessing combustion condition of a combustion apparatus including restriction of a blowing value; and

FIG. 14 is a sectional perspective view conceptually illustrating a structure of a modified combustion apparatus in which the second ion current measuring element is located at a different position from those in FIGS. 1 and 8 and the first ion current measuring element is different from those in FIGS. 1 and 12 of the present invention

DESCRIPTION OF THE PREFERRED EMBODIMENT

Now, an embodiment of the present invention will be described below in detail, making reference to the accompanying drawings. First, an outline configuration and basic functions of a combustion apparatus of the present invention will be described, referring to a schematic view of FIG. 1. FIG. 1 is a sectional perspective view conceptually illustrating a configuration of a combustion apparatus 1 of the present invention.

In the following descriptions, the vertical positional relationship is based on a combustion apparatus 1 positioned upright and producing flame at an upper part thereof. Terms “upstream” and “downstream” are based on an air or fuel gas flow. A “width direction” denotes a lateral direction (a direction of an arrow “W” in the figure) with a part having the maximal area of the combustion apparatus 1 facing the front.

The combustion apparatus 1 of the present embodiment may be used by unitizing more than one apparatus accommodated in a casing or alone. The combustion apparatus 1 includes a premixer 2, a burner port assembly 3, and two air passage members 5. In the combustion apparatus 1, the premixer 2 and the burner port assembly 3 are engaged with each other to constitute an intermediate member 6, which is interposed between the two air passage members 5. However, in the actual use, a plurality of the air passage members 5 and a plurality of the intermediate members 6 are alternately arranged to form a planar shape in an order such as the air passage member 5, the intermediate member 6, the air passage member 5, the intermediate member 6, the air passage member 5, and so on.

The premixer 2, a component of the combustion apparatus 1, serves to premix fuel gas and air therewithin. The premixer 2 includes a mixing part 7 having a curved passage and an aperture row part 10 having apertures 8 arranged in a row. The aperture row part 10 has a cavity of a substantially square shape in a cross section extending lengthwise and straight.

FIG. 7 is a cross section of the air passage member 5 of the present embodiment, showing air flow therewithin. The air passage member 5 generally has a thin wall shape. The air passage member 5 is constituted by a first face 11 and a second face 12, each made of a thin plate, in such a manner that the first and the second faces 11 and 12 are connected with forming a narrow gap therebetween, the three sides except the bottom face being joined, thereby defining a cavity to be an air passage 13 inside.

Specifically, the first face (front plate) 11 and the second face (rear plate) 12 are made by folding a unitary plate. The distal end where the front plate and the rear plate meet has a sharply-angled bent portion 14, the bent portion 14 making up a top portion 9, which extends in ridge-like lines.

The proximal end of the air passage member 5 is opened between the plates of the first and the second faces (front and rear plates) 11 and 12, forming an air inlet 15.

In the air passage member 5, apertures for discharging air are formed at three areas. In the case that a plurality of the combustion apparatus 1 are arranged in parallel as described above, the air passage members 5 and the intermediate members 6 are alternately arranged to form a planar shape. The same numbers of apertures are formed at the same portions of the first and the second faces 11 and 12 of each air passage member 5.

The apertures for discharging air are formed at the distal end, a position facing to a first combustion part 46, and a position facing to the intermediate member 6, roughly describing.

Specifically, the plates of the first face (front plate) 11 and the second face (rear plates) 12 of the air passage member 5 are paralleled in their most parts, but are angularly folded at their distal ends, forming inclined surfaces 16 and 17 at the first and the second faces, respectively. The inclined surfaces 16 and 17 each have distal apertures (secondary air supply openings) 20. Further, distal apertures (secondary air supply openings) 21 are formed at a tip (ridge line). The distal apertures 20 and 21 are disposed for supplying a secondary air 67 to a secondary flame 68. In FIG. 1, the secondary flame 68 is drawn inward from the tip of the air passage member 5 due to space limitation, but actually extends outward (upward in FIG. 1) from the tip of the air passage member 5.

The first and the second surfaces 11 and 12 of the air passage member 5, as shown in FIG. 1, have the air passage 13 formed in such a manner as being narrower at the distal end than at the proximal end and having steps at positions corresponding to the proximal end of the first combustion part 46, which steps also constitute inclined surfaces 22. Air emission apertures (air supply ports, secondary air supply openings) 23 facing to a combustion part are formed at each of the steps. The air emission apertures 23 are designed to supply a secondary air therethrough to a primary flame 24 of the first combustion part 46, so as to burn part of the primary flame 24 to produce the secondary flame 68 within a part of the first combustion part 46.

Further, air emission apertures (upstream air emission apertures) 48 are formed at a position facing to the intermediate member 6 of the first and the second surfaces 11 and 12 of the air passage member 5, and whereby air is supplied to each side of the burner port assembly 3, so as to achieve flame stabilizing.

The burner port assembly 3 is mainly constituted by a main body 25 and decompression walls 26. The main body 25 of the burner port member 3 is made by bending a piece of metal plate. The main body 25 has a top face 30 functioning as a burner port and two side walls 31 and 32 communicating with the top face 30 and bent at substantially 90 degree angle with respect to the top face 30. Right and left sides of the burner port assembly 3 are closed with only a bottom face in the figure opened. The top face 30 of the burner port assembly 3 (or the main body 25) has an elongated shape with an A-line shape cross section and has slits regularly arranged. The slits constitute burner ports 33. The burner ports 33 formed at the main body 25 (or the top face 30) functions as “central apertures.”

The side walls 31 and 32 each have a protruding part 34 protruding outwards (in a thickness direction) at its intermediate portion. The protruding part 34 is formed across the full width of the burner port assembly 3.

Open ends of the side walls 31 and 32 are bent twice at a 90 degree angle as shown in FIG. 1, each forming outside a trough (or a gutter) 38 for engagement. The troughs 38 have bottom walls 36 vertical to and outer walls 37 parallel to the respective side walls 31 and 32.

The decompression walls 26 are attached to the main body 25, as described above. The decompression walls 26 are fixed to the respective side walls 31 and 32 of the main body 25, forming gaps 29 between the respective side walls 31 and 32 of the main body 25. The gaps 29 each have an opening at a top of the figure. The opening functions as a side opening 27.

Apertures 35 are formed at the side walls 31 and 32 and at positions facing to the decompression walls 26. The gaps 29 communicate with an inner space of the main body 25 via the apertures 35.

Next, a relationship between components will be described below.

FIG. 6 is an exploded perspective view of the combustion apparatus 1. Referring to FIG. 6, the combustion apparatus 1 arranges the premixer 2 and the burner port assembly 3 between the two air passage members 5.

In the present embodiment, as shown in FIG. 1, the premixer 2 and the burner port assembly 3 are engaged, thereby constituting the intermediate member 6. More specifically, the aperture row part 10 of the premixer 2 is placed between the side walls 31 and 32 of the burner port assembly 3. In the actual producing process, the premixer 2 is inserted from an opening (bottom in the figure) between the side walls 31 and 32 of the burner port assembly 3 to join the both members.

The side walls 31 and 32 and the aperture row part 10 have partly contact with each other by their convex and concave shapes not shown. Specifically, the aperture row part 10 is interposed between the side wall 31 and the side wall 32 via convex and concave, with the premixer 2 and the burner port assembly 3 unified. As described above, the side walls 31 and 32 and the aperture row part 10 have partly contact with each other by their convex and concave shapes, and in other words, they partly keep away from each other. The cross section in FIG. 1 shows a cross section at a site where the side walls 31 and 32 and the opening row part 10 keep away from each other.

Sites corresponding to the protruding parts 34 of the side walls 31 and 32 are away from the accommodated opening row part 10. The protruding parts 34 each are opposite to a row of apertures 8 of the aperture row part 10. Thus, outsides of the apertures 8 of the aperture row part 10 keep away from the side walls 31 and 32, so as to form spaces (mixing spaces) 39 wider than the other portions. The spaces 39 are formed so as to be opposite to all the apertures 8.

A relatively large space 47 is formed between the side walls 31 and 32 and between the top of the aperture row part 10 and the top face 30 of the burner port assembly 3. In the present embodiment, the mixing spaces 39 and the space 47 downstream of the aperture row part 10 form a burner port upstream passage 49.

The air passage members 5 are attached to the both sides of the intermediate member 6. Each of the air passage members 5 is joined with the intermediate member 6 by engaging the air inlet 15 of its proximal end with the trough 38 of the burner port assembly 3. Specifically, the outer wall 37 of the trough 38 is inserted into the air inlet 15 and the tip (the bottom edge in the figure) of the air passage member 5 is inserted into the trough 38, and whereby the air passage member 5 is brought into contact with the bottom wall 36 of the trough 38.

The air passage member 5 and the intermediate member 6 (the burner port assembly 3) have partly contact with each other by the convex and concave shape, and thus the both members are unified. The both members have partly contact with each other as just described, and in other words, keep partly away from each other. The cross section of FIG. 1 shows a site where the air passage member 5 and the intermediate member 6 (burner port member 3) keep away from each other so as to facilitate understanding their functions. However, at an end (the bottom edge in the figure) upstream of the combustion apparatus 1, a space 40 between the air passage member 5 and the intermediate member 6 are closed by the bottom wall 36 of the trough 38. Thus, the space 40 does not directly communicate with outside at the proximal end.

The burner port assembly 3 is interposed between the two air passage members 5 as described above, the top face 30 of the assembly 3 lying below (in the figure) the top level of the air passage members 5 and, so to say, buried between the air passage members 5. Therefore, a space ahead (downstream) of the top face 30 of the assembly 3 is partitioned by walls of two air passage members 5. In the present embodiment, a space enclosed by the top face 30 of the assembly 3 and two air passage member 5 functions as the first combustion part 46.

A first ion current measuring element (probe) 65 and a second ion current measuring element (probe) 66, which are characteristic constituents of the present invention, are incorporated in the combustion apparatus 1 described above. Specifically, the first ion current measuring element 65 is arranged along a longitudinal direction of the combustion apparatus 1 within the first combustion part 46 above the burner port assembly 3 and interposed between two opposing air passage members 5 and at a site where the primary flame 24 is to take place in combustion. The second ion current measuring element 66 is arranged adjacent to the bent portion 14 at the distal end of the air passage member 5. The first and the second ion current measuring element 65 and 66 are secured to walls (not shown) partitioning the first combustion part 46 at a near side or a far side of paper.

Flame has ions of burning components, being electrically conductible. The first and the second ion measuring elements 65 and 66 take advantage of this nature of flame.

Herein, the first measuring element 65 penetrates through flame front with its distal end positioned within the primary flame 24. The primary flame 24 includes therein unburned gas mixture, so that the temperature is lower therein than at the flame front. Thus, the first measuring element 65 does not reach an extremely high temperature in totality. Further, the second ion current measuring element 66 is arranged at a position where the secondary air 67 supplied (etted) through the distal apertures (secondary air supply openings) 21 of the bent part 14 encounters (viz. adjacent to the distal apertures 21). Therefore, the second measuring element 66 is enveloped by the secondary air 67, not being exposed to the secondary flame 68.

The secondary air 67 restricts an increase in temperature of the second measuring element 66. Further, the secondary air 67 cuts off an electrical connection produced by flame of the first and the second measuring elements 65 and 66 during a normal combustion. Specifically, an ion current does not pass between the first and the second measuring elements 65 and 66, so that detection of an anomalous combustion when an amount of air becomes short to an amount of combustion gas is ensured.

FIG. 5 is a sectional view of the combustion apparatus in FIG. 2. FIG. 5 illustrates a condition in which the first and the second measuring elements 65 and 66 are arranged in the combustion apparatus 1, as described above.

Procedures for assessing combustion condition using the first and the second ion current measuring elements 65 and 66 will be described in detail below, making reference to FIGS. 9 to 11. FIG. 9 is a graph showing a relation of output values (microampere: μA) of the first and the second ion current measuring elements 65 and 66 and an amount of carbon monoxide CO (ppm). FIG. 10 is a view of a controlling system for controlling an amount of air and an amount of fuel gas. FIG. 11 is a flow chart for assessing combustion condition of a combustion apparatus.

As shown in FIG. 9, a regulation value of carbon-monoxide CO emissions is set so as to meet environmental standards. Specifically, the regulation value of emissions (threshold value) corresponds to a value (μA) of difference between output values measured by the first and the second measuring elements 65 and 66.

In FIG. 9, during a normal combustion, there are many ions in the primary flame 24 generated by combustion, so that an output value measured by the first measuring element 65 (measured ion current value) becomes higher. In contrast, most of the second measuring element 66 is enveloped by the secondary air 67 and ion generation therearound is extremely few, so that an output value measured by the second measuring element 66 becomes much lower than that measured by the first measuring element 65 even though the secondary flame 68 principally involving combustion of a carbon monoxide CO or a hydrogen H exists.

If and when only an amount of air supplied by means of a fan 41 is reduced for some reasons, an amount of emissions of unburned combustible component is increased in the first combustion part 46. Additionally, stretch of the primary flame 24 causes an increased portion of the first measuring element 65 located within the primary flame 24 enveloped by unburned gas mixture, but a combustion temperature goes down, resulting in a lower ion concentration, whereby an output value measured by the first measuring element 65 drops to a lower value.

In contrast, an output value measured by the second measuring element 66 is increased because a carbon monoxide CO component generated by lack of air in the primary flame 24 reaches the second measuring element 66. Thus, a value of difference between output values measured by the first and the second ion current measuring elements 65 and 66 increases with decrease in an amount of air (air volume) supplied by means of the fan 41.

Therefore, a calculated value of difference D between both output values corresponding to a regulation value X (FIG. 9) of emission concentration of carbon monoxide CO is obtained in advance by an experiment. The calculated value is stored as a threshold value (a standard value relating to output values) in a memory 76 incorporated in a control device 69 shown in FIG. 10.

Then, a CPU 74 calculates a difference between output values measured by the first and the second measuring elements 65 and 66, and further, compares the calculated value and the threshold value stored in the memory 76.

If the calculated value is smaller than the threshold value, the control device 69 determines that combustion by the combustion apparatus 1 is normal. If the calculated value reaches or exceeds the threshold value, the control device 69 determines that combustion by the combustion apparatus 1 is anomalous. If and when the control device 69 determines (assesses) combustion as an anomaly, the control device 69 increases air blowing volume of the fan 41 or decreases an amount of fuel gas jetted from a nozzle 42 shown in FIG. 1 by closing a fuel gas supply valve 59 or a fuel gas proportional valve 18, thereby normalizing the combustion. Herein, the threshold value may have a predetermined width “d” so that combustion is determined as an anomaly when the calculated value falls within a threshold value range (FIG. 9). Specifically, the width “d” may be set to a width of a concentration of carbon monoxide CO lower than a regulation value “X” so that combustion is determined as an anomaly before the calculated value reaches the regulation value “X.”

Normalization of combustion after the control device 69 determines the combustion as an anomaly and takes measures as described above, the combustion device 69 adjusts the fan 41 or an opening degree of the fuel gas supply valve 59 or the fuel gas proportional valve 18 so as to prevent the calculated value from reaching the threshold value. Instead, it is also possible to increase or decrease a total amount of air supplied by means of the fan 41 or regulate the air allocation to each of a first, a second, a third routes described below. Alternatively, an amount of fuel gas jetted from the nozzle 42 may be regulated. Then, promotion of awareness to users by means such as blinking an alarm lamp in the case that the control device 69 determines combustion as an anomaly facilitates a rapid and appropriate maintenance.

A series of operations described above will be described in detail below, referring to a flow chart in FIG. 11.

Starting of operations of the combustion apparatus 1 activates the fan 41 first, and next, fuel gas is jetted from the nozzle 42 (FIG. 1) to produce a gas mixture within the premixer 2. Then, the gas mixture is ignited by an igniter 4 (FIG. 10), whereupon the above-mentioned primary and secondary combustions are performed.

The control device 69 calculates a calculated value (difference between both output values) from output values measured by the first and the second ion current measuring elements 65 and 66, so as to compare the calculated value with a threshold value stored in the memory 76. If the calculated value does not reach the threshold value (or the threshold value range), the control device 69 determines the combustion as an anomaly. Then, the control device 69 determines whether the calculated value reaches the threshold value or not at predetermined time intervals (for example, 0.05 to 3 second interval, or preferably 0.1 to 1 second interval) during the operations of the combustion apparatus 1. If the calculated value reaches the threshold value (or the threshold range), the combustion is determined as an anomaly, whereupon the control device 69 increases air blowing volume by means of the fan 41 or decreases an amount of supplied fuel gas. Further, the control device 69 measures ion current values (output values) using the first and the second measuring elements 65 and 66 to calculate a calculated value, so as to confirm improvement of combustion condition. If the combustion condition is not improved, these procedures are repeated until the condition is improved. After improvement of the combustion condition, determination whether the calculated value is lower than the threshold value or not is carried out at predetermined time intervals and is brought to completion upon stopping of the operations of the combustion apparatus 1.

According to a control in the flow chart in FIG. 11, the difference (calculated value) between the output values is compared with the threshold value and operations such as increasing air blowing volume by means of the fan 41 are performed when the calculated value exceeds the threshold value. However, in the case of excessively increased air blowing volume, the volume would be preferably decreased to an appropriate amount.

Further, in the case of excessively restricted fuel gas supply, the gas supply would be preferably increased to an appropriate amount.

As shown in a flow chart in FIG. 13, for example, a second threshold value can be set, so as to decrease air blowing volume by the fan 41 or increase fuel gas supply when the calculated value falls below the second threshold value.

Herein, FIG. 13 is a flow chart for assessing combustion condition of a combustion apparatus including restriction of a blowing value.

In the case that output values measured by the first and the second ion current measuring elements 65 and 66 fail to fall within an estimated appropriate range even after increasing or decreasing of air blowing volume or fuel gas supply, combustion would be preferably stopped.

It is possible to have an alarm device for giving some alarm when difference (calculated value) between output values measured by the first and the second measuring elements 65 and 66 exceeds a threshold value.

A function of the combustion apparatus 1 provided with such the first and the second ion current measuring elements 65 and 66 will be described in detail below.

A number of the combustion apparatus 1 are apposed within a casing 54 as shown in FIG. 3, with air being sent by means of the fan 41 from a bottom side in FIG. 1. Fuel gas is introduced into the apparatus 1 through a gas inlet 43 of the premixer 2 by means of the nozzle 42.

First, air stream will be described. The air stream is shown by thin lines in FIG. 1.

Air blow generated by the fan 41 is straightened through openings 45 of a straightening vane 44 to be introduced into the combustion apparatus 1 through the proximal end (bottom in the figure) of the apparatus 1.

There are three routes for air to be introduced into the apparatus 1. The first route passes through inside the air passage member 5, the air flowing through the air inlet 15 formed at the proximal end of the air passage member 5 into the air passage member 5 and going up (toward downstream) to the distal end through the air passage 13 of the air passage member 5.

Most of the air is discharged outside through the distal apertures 20 and 21.

Part of the air flowing in the air passage member 5 is discharged through the air emission apertures 23 facing to a combustion part and the air emission apertures (upstream air emission apertures) 48.

Air directed diagonally to the front of an axis line of the apparatus 1 is discharged through the air emission apertures 23 of the inclined surfaces 22.

Further, the air discharged through the air emission apertures 48 flows in the space 40 between the air passage member 5 and the intermediate member 6 to the side of the burner port assembly 3.

The second route passes through inside the intermediate member 6.

The intermediate member 6 has such a configuration that the aperture row part 10 of the premixer 2 is interposed between the side walls 31 and 32 of the burner port assembly 3. Gaps exist between the aperture row part 10 and the burner port assembly 3 and are open at their bottoms (upstream) to form openings 28. The air is entered through the openings 28.

The air having entered through the openings 28 enters the mixing spaces 39 through the gaps between the side walls 31 and 32 and the aperture row part 10, reaching the space 47 between the aperture row part 10 and the top face 30 of the burner port assembly 3. That is, the air described above flows in the burner port upstream passage 49. Finally, the air is discharged through the slits, i.e., the burner ports 33, to the first combustion part 46. Part of the air having entered the space 47 enters the gaps 29 between the main body 25 and the side walls 31 and 32 through the apertures 35 formed at the side walls 31 and 32 of the main body 25 and is discharged to the first combustion part 46 through the side openings 27.

The third route is a route for the primary air, which is introduced with fuel gas through the gas inlet 43 of the premixer 2. The third route is the same route as that of fuel gas (gas mixture) flow, being described below as fuel gas flow. The fuel gas flow is shown by solid arrowed lines in FIG. 1.

Fuel gas is introduced with the primary air into the gal inlet 43 of the premixer 2 and mixed with air in the mixing part 7 to be flown into the aperture row part 10. The aperture row part 10 has a number of apertures 8 arranged linearly, so that the fuel gas (gas mixture) having introduced thereinto is evenly discharged through each of the apertures 8. The fuel gas (gas mixture) having been discharged through the apertures 8 of the row part 10 enters the mixing spaces 39 formed between the side walls 31 and 32 of the burner port assembly 3 and the row part 10 to be mixed with air flowing in the second route, reaching the burner port upstream passage 49.

The air flowing in the second route flows vertically (from bottom to top), whereas the fuel gas (mixed gas) having been discharged through the apertures 8 of the row part 10 flows in a direction perpendicular to the air flow. Thus, the fuel gas (gas mixture) hits hard the air at the mixing spaces 39, and whereby mixing of the fuel gas with the air is facilitated. Further, each of the mixing spaces 39 extends throughout in a longitudinal direction of the aperture row part 10, thereby smoothing pressure.

After having passed through the mixing spaces 39, the fuel gas (gas mixture) is flown into the space 47, during which the mixing of the fuel gas (gas mixture) with the air is enhanced. After that, the fuel gas flows in the same way as the flow in the burner port upstream passage 49, entering the space 47 between the aperture row part 10 and top face 30 of the burner port assembly 3, and being mostly discharged through the slits (the burner ports) 33 to the first combustion part 46. Part of the air having entered the space 47 enters the gaps 29 between the decompression walls 26 and the sidewalls 31 and 32 of the main body 25 through the apertures 35 formed at the side walls 31 and 32, being discharged through the side openings 27 to the first combustion part 46.

The fuel gas (gas mixture) discharged through the burner ports 33 are mixed with air within the premixer 2 and further mixed with air having flown through the second route within the mixing spaces 39, and thus, being uniformed and being discharged through the burner ports 33 at a uniform rate.

However, though fuel gas (gas mixture) discharged through the burner ports 33 is mixed with air, an amount of the air is below a theoretical amount of air. That is why fuel gas (gas mixture) discharged through the burner ports 33 is in an oxygen-deficient condition, failing in achieving complete combustion.

Ignited, the fuel gas (gas mixture) produces the primary flame 24 at the first combustion part 46, so as to perform a primary combustion. However, the fuel gas is not completely burned because of insufficient oxygen as described above, resulting in generating a great deal of unburned combustible component.

The unburned combustible component is discharged outside through an opening of the first combustion part 46. Herein, air is supplied to outside of the first combustion part 46 through the distal end (distal apertures 20 and 21) of the air passage member 5. Therefore, the unburned combustible component performs a secondary combustion upon oxygen (the secondary air 67) supply. In other words, an area outside of the first combustion part 46 functions as a secondary combustion part and produces the secondary flame 68.

Further, in the present embodiment, air is supplied to the proximal end of the primary flame 24, so as to produce an auxiliary flame in the proximal end of the primary flame 24.

In the present embodiment, fuel gas is discharged to the primary combustion part 46 not only through the burner ports 33, i.e., the “central openings,” but also through the side openings 27. However, the flow rate of fuel gas discharged through the side openings 27 is slower than that discharged through the burner ports 33. Specifically, fuel gas to be discharged through the side openings 27 enters the gaps 29 between the decompression walls 26 and the side walls 31 and 32 of the main body 25 through the apertures 35 formed at the side walls 31 and 32, being discharged through the side openings 27 to the first combustion part 46. That restricts an amount of fuel gas entering the gaps 29. As a consequence, fuel gas discharged through the side openings 27 is small in amount, whereas the side openings 27 each have a large opening space. Thus, fuel gas discharged through the side openings 27 has a low flow rate.

Further, as described above, part of air passing though the air passage member 5, which is the first route, is discharged through the air emission apertures (upstream air emission apertures) 48 to the space 40 between the air passage member 5 and the intermediate member 6, reaching the side faces of the burner port assembly 3. Therefore, the side faces of the assembly 3 is richer in oxygen than other parts, ensuring that fuel gas discharged through the side openings 27 performs relatively stable combustion with reception of air supply.

Coupled with a low flow rate of fuel gas as described above, a stable auxiliary flame is produced in the vicinity of the side openings 27. The proximal end of the primary flame 24 is held by small flame produced in the vicinity of the side openings 27.

Still further, in the present embodiment, air having been discharged through the combustion part-facing air emission apertures 23 stabilizes the secondary flame 68. Specifically, in the present embodiment, the inclined surfaces 22 are located at the first and the second faces 11 and 12 of the air passage member 5 and at a site corresponding to the proximal ends of the first combustion part 46. The air emission apertures 23 are formed at the inclined surfaces 22, thereby supplying air diagonally to an air direction from the proximal end of the first combustion part 46. Thus, the supplied air is supplied to the first combustion part 46 without obstructing the primary flame 24 or the flow of unburned gas. As a consequence, part of unburned gas within the first combustion part 46 starts combustion and partly produces a secondary flame, which merges with the external secondary flame 68, thereby stabilizing the secondary flame 68 produced outside.

Yet further, in the present embodiment, the air emission apertures 23 are diagonally open, so that air discharged through the air emission apertures 23 does not obstruct the primary flame 24 or the flow of unburned gas, as described above. Consequently, the secondary flame 68 is stably produced at a distance from the air passage member 5 and does not excessively heat the air passage member 5.

The combustion apparatus 1 of the present embodiment therefore stabilizes both the primary and the secondary flames 24 and 68 and is practical.

The first and the second ion current measuring elements 65 and 66 are designed to be incorporated in a two-staged combustion apparatus adapted to perform a primary combustion in an oxygen-deficient condition and a secondary combustion with further supply of a secondary air.

Now, a more practical configuration example of the present invention will be described in referring to the following figures after FIG. 2. FIG. 2 is a perspective view of a combustion apparatus in a practical embodiment of the present invention. FIG. 3 is a plan view of a plurality of the combustion apparatus in FIG. 2 accommodated in a casing. FIG. 4 is a sectional view taken substantially along the lines IV-IV of FIG. 3. The embodiment described below is practically designed for embodying the present invention and has a most recommended configuration.

A combustion apparatus shown in the figures following after FIG. 2 has the same basic configuration and basic function as that in the above-mentioned embodiment, but is practically designed to detail. The same numerals are assigned to components that carry out the same functions as those in the foregoing embodiment, and descriptions of the duplicated functions are simplified.

A plurality of combustion apparatus 1 shown in FIG. 2 are accommodated in parallel in a casing 54 as shown in FIGS. 3 and 4. Each of the combustion apparatus 1 of the present embodiment also includes a premixer 2, a burner port assembly 3, and air passage members 5. The premixer 2 and the burner port assembly 3 are engaged to constitute an intermediate member 6, which is interposed between the two air passage members 5.

The air passage member 5 has apertures for emitting air at three areas. The areas consist of the distal end, a position facing to the first combustion part 46, and a position facing to the intermediate member 6, roughly describing.

In the combustion apparatus as described above, fuel gas and air are appropriately and ideally distributed, thereby performing stable production of the primary flame 24 and the secondary flame 68. However, if the fan 41 might break down and air blowing volume might be reduced, a ratio (equivalent ratio) of an amount of fuel gas and that of air (amount of oxygen) might change, leading to worsening of combustion condition. However, according to the combustion apparatus 1 of the present invention, an anomaly of combustion condition is certainly detected by ion current values (output values) measured by the first and the second ion current measuring elements 65 and 66. Oxygen partial pressure in the air is reduced (viz. oxygen is reduced) when the combustion apparatus 1 runs in a closed chamber, but even in this case, the combustion apparatus embodying the present invention immediately detects an anomaly of combustion condition.

Therefore, immediately after detection of an anomaly, the control device 69 increases air blowing volume by the fan 41 or reduces an opening degree of the fuel gas proportional valve 18 or the fuel gas supply valve 59 so as to reduce an amount of fuel gas, thus normalizing combustion.

The first and the second ion current measuring elements 65 and 66 provided in the combustion apparatus described above may be curved or bent at their distal end as shown in FIG. 8, for example, instead of being of a straight shape. FIG. 8 is a sectional perspective view of a combustion apparatus arranged with ion current measuring elements different from those in FIG. 1. The curved or bent distal end detects combustion condition of the primary flame 24 or the secondary flame 68 more certainly.

For example, a curved or bent (flexed) distal end 65 a of the first ion current measuring element 65 is oriented toward the slits (burner ports 33) (downwardly, or upstream), and a curved or bent (flexed) distal end 66 a of the second ion current measuring element 66 is oriented toward the center of the first combustion part 46 (viz. the area where the primary or the secondary flame 24 or 68 is formed) and slightly upstream.

When the primary flame 24 comes up due to a shortage of air, the curved or bent (flexed) distal end 66 a of the second measuring element 66 ensures the effect to detect coming-up of the primary flame 24 even if combustion is small in amount and the primary flame 24 is small. The distal end 66 a of the second measuring element 66 curved below the horizon exerts the above-mentioned effect more than one curved horizontally toward the center of the primary flame 24 because one curved above the horizon weakens the above-mentioned effect.

However, the distal end 66 a curved below the horizon shortens a distance between the distal end 66 a and the secondary air supply openings. In view of such a possibility that the distal end 66 a hangs downward because of a high temperature of the second measuring element 66 caused by an anomalous combustion, it is preferable to curve the distal end 66 a toward the center of the primary flame 24 at the horizon.

In the example described above, the second ion current measuring element 66 is located adjacent to the secondary air jetting apertures (distal apertures 20, 21, 63, and 64) at the distal end of the air passage member 5, but, as shown in FIG. 12, may be located adjacent to the air emission apertures 23 facing to a combustion part. FIG. 12 is a sectional perspective view of a modified combustion apparatus in which the second ion current measuring element is located at a different position from those in FIGS. 1 and 8. Being located adjacent to the air emission apertures 23, the second ion current measuring element 66 is enveloped in the secondary air supplied from the air emission apertures 23 and is not exposed to flame, so that an excessive increase in temperature of the second measuring element 66 is avoided. That avoids high-temperature deformation of the second measuring element 66. Further, a secondary air 67 a supplied from the air emission apertures 23 and blown to the second measuring element 66 prevents approach of ions in flame to the element 66, and further prevents conduction between the first and the second measuring elements 65 and 66 despite close approach thereof in a vertical direction, thereby ensuring detection of a shortage of an amount of air. Thus, anomalous combustion of the combustion apparatus 1 is accurately detected.

FIG. 14 is a sectional perspective view conceptually illustrating a structure of a modified combustion apparatus in which the second ion current measuring element is located at a different position from those in FIGS. 1 and 8 and the first ion current measuring element different from those in FIGS. 1 and 12. In the combustion apparatus 1 shown in FIG. 14, the second measuring element 66 is located adjacent to the air emission apertures 23 facing to the combustion part (secondary air supply apertures) and a configuration except the device 66 is the same as that of the combustion apparatus 1 shown in FIG. 1. In the example shown in FIG. 14, the distal end of the first measuring element 65 is curved or bent below, as described above.

In the present embodiment, the air emission apertures 23 open in an oblique direction, so that, as described above, the secondary air 67 a does not interrupt the primary flame 24 or the flow of unburned gas, thereby producing the secondary flame 68 at a point distant from the air passage member 5, which is not excessively heated. Further, the secondary air 67 a is blown to the second measuring element 66, thereby cooling the device 66.

Consequently, the combustion apparatus 1 of the present embodiment stabilizes the primary and the secondary flames 24 and 68 and certainly detects combustion condition, being practical.

INDUSTRIAL APPLICABILITY

The combustion apparatus of the present invention is applied in a device requiring heating such as a water heater or a bath heater. 

1. A combustion apparatus adapted to perform a primary combustion of air-fuel mixture in an oxygen-deficient condition composed of mixture of primary air and fuel gas and further perform a secondary combustion upon supply of secondary air, comprising: a first ion current measuring element positioned at a site where a flame of the primary combustion is to take place; and a second ion current measuring element adjacent to a secondary air supply opening for supplying the secondary air, so as to control at least one of supplied air and fuel gas based on measured values by the first and the second ion current measuring elements.
 2. The combustion apparatus as defined in claim 1, being adapted to control at least one selected from a group consisting of (a) a ratio of an amount of the primary air to that of the secondary air, (b) a total amount of the primary and the secondary air, and (c) an amount of the fuel gas.
 3. The combustion apparatus as defined in claim 2, further comprising a memory storing a standard value relating to difference between output values measured by the first and the second ion current measuring elements corresponding to a regulation value of emission concentration of carbon monoxide, being adapted to compare a calculated value of the difference with the standard value stored in the memory, and being adapted to perform one selected from a group consisting of (a) increasing a ratio of amount of the secondary air to that of the primary air, (b) increasing a total amount of the primary and the secondary air, and (c) reducing fuel gas supply, in the case that the calculated value is bigger than the value stored in the memory.
 4. The combustion apparatus as defined in claim 1, comprising: at least one premixer adapted to introduce thereinto the fuel gas along with the primary air to generate the air-fuel mixture in an oxygen-deficient condition; at least one air passage member of a wall shape having the secondary air supply opening for supplying the secondary air at its distal end; at least one burner port assembly arranged between two of the air passage members or between the air passage member and another wall; and at least one combustion part formed by a space enclosed by the burner port assembly and the air passage member, wherein the air-fuel mixture is discharged from the burner port assembly into the combustion part to perform the primary combustion and further perform the secondary combustion upon supply of the secondary air from the secondary air supply opening of the air passage member.
 5. The combustion apparatus as defined in claim 4, defining three routes through which air flows: a first route within the air passage member, a second route from between the premixer and the burner port assembly to the combustion part, and a third route through which air flows with the fuel gas, the first and the second routes being adapted to supply the secondary air, the third route being adapted to introduce the primary air, further comprising a memory for storing a standard value relating to difference between output values measured by the first and the second ion current measuring elements corresponding to a regulation value of emission concentration of carbon monoxide, being adapted to compare a calculated value of the difference with the standard value stored in the memory, and being adapted to increase supply of the secondary air flowing through the first and the second routes in the case that the calculated value is bigger than the standard value stored in the memory.
 6. The combustion apparatus as defined in claim 1, being adapted to blow air to the second ion current measuring element.
 7. The combustion apparatus as defined in claim 1, wherein the first and the second ion current measuring elements have 15 each a distal end, the distal end of the first ion current measuring element being curved or bent toward the upstream of fuel gas flow, and the distal end of the second ion current measuring element being curbed or bent toward the center of a combustion zone.
 8. The combustion apparatus as defined in claim 1, further comprising a memory storing a standard value relating to difference between output values measured by the first and the second ion current measuring elements corresponding to a regulation value of emission concentration of carbon monoxide.
 9. The combustion apparatus as defined in claim 8, the standard value having a predetermined width.
 10. The combustion apparatus as defined in claim 8, being adapted to compare a calculated value of the difference with the standard value stored in the memory.
 11. The combustion apparatus as defined in claim 10, being adapted to increase air supply and/or reduce fuel gas supply in the case that the calculated value is bigger than the standard value stored in the memory.
 12. A combustion apparatus adapted to perform a primary combustion of air-fuel mixture in an oxygen-deficient condition composed of mixture of primary air and fuel gas and further perform a secondary combustion upon supply of secondary air, comprising: a first ion current measuring element positioned at a site where a flame of the primary combustion is to take place; an air supply port for supplying air different from the primary air to a base of the flame of the primary combustion; and a second ion current measuring element adjacent to the air supply port, so as to control at least one of supplied air and fuel gas based on measured values by the first and the second ion current measuring elements.
 13. The combustion apparatus as defined in claim 12, being adapted to control at least one selected from a group consisting of (a) a ratio of an amount of the primary air to that of the secondary air, (b) a total amount of the primary and the secondary air, and (c) an amount of the fuel gas.
 14. The combustion apparatus as defined in claim 12, being adapted to blow air to the second ion current measuring element.
 15. The combustion apparatus as defined in claim 12, further comprising: at least one premixer adapted to introduce thereinto the fuel gas along with the primary air to generate the air-fuel mixture in an oxygen-deficient condition; at least one air passage member of a wall shape having a secondary air supply opening for supplying the secondary air; at least one burner port assembly arranged between two of the air passage members or between the air passage member and another wall; and at least one combustion part formed by a space enclosed by the burner port assembly and the air passage member, wherein the air-fuel mixture is discharged from the burner port assembly into the combustion part to perform the primary combustion.
 16. The combustion apparatus as defined in claim 15, being adapted to blow air to the second ion current measuring element.
 17. The combustion apparatus as defined in claim 14, defining three routes through which air flows: a first route within the air passage member, a second route from between the premixer and the burner port assembly to the combustion part, and a third route through which air flows with the fuel gas, the first and the second routes being adapted to supply the secondary air, the third route being adapted to introduce the primary air, further comprising a memory for storing a standard value relating to difference between output values measured by the first and the second ion current measuring elements corresponding to a regulation value of emission concentration of carbon monoxide, being adapted to compare a calculated value of the difference with the standard value stored in the memory, and being adapted to increase supply of the secondary air flowing through the first and the second routes in the case that the calculated value is bigger than the standard value stored in the memory.
 18. The combustion apparatus as defined in claim 17, being adapted to blow air to the second ion current measuring element.
 19. A combustion apparatus adapted to perform a primary combustion of air-fuel mixture in an oxygen-deficient condition composed of mixture of primary air and fuel gas and further to facilitate combustion upon supply of air different from the primary air, comprising: a first ion current measuring element positioned at a site where a flame of the primary combustion is to take place; an air supply port for supplying the air different from the primary air; and a second ion current measuring element adjacent to the air supply port, so as to control at least one of supplied air and fuel gas based on measured values by the first and the second ion current measuring elements.
 20. The combustion apparatus as defined in claim 19, being adapted to blow air to the second ion current measuring element. 